8.3 Fossil Fuel Power Production (Aki and Coby)

1 hour
8.3.1 Outline the historical and geographical reasons for the widespread use of fossil fuels.
8.3.2 Discuss the energy density of fossil fuels with respect to the demands of power stations.
8.3.3 Discuss the relative advantages and disadvantages associated with the transportation and storage of fossil fuels.
8.3.4 State the overall efficiency of power stations fueled by different fossil fuels.
8.3.5 Describe the environmental problems associated with the recovery of fossil fuels and their use in power stations.

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8.3.1 Outline the historical and geographical reasons for the widespread use of fossil fuels.

Students should appreciate that industrialization led to a higher rate of energy usage, leading to industry being developed near to large deposits of fossil fuels.

Geographical Reasons

• Coal - Coal reserves are found on every continent
• Oil - Oil reserves are concentrated in the Middle East and South America
• Natural Gas - recoverable reserves of gas are more widely spread throughout the world than oil.

Historical Reasons:

Industrialization led to marked increase in energy consumption. Thus, industries were established close to fuel reserves. Coal was the most versatile because it can be used directly and can also be modified into coke and used for industries such as steel production. Natural gas was also commonly used for supplying energy for cooking, warming houses, and lighting of houses.

8.3.2 Discuss the energy density of fossil fuels with respect to the demands of power stations.

Students should be able to estimate the rate of fuel consumption by power stations.

Fuel	Energy Density (Coals when dried)
	Solid or Liquid		Gas
	MJ Kg^-1	MJ dm^-1	MJ dm^-1
natural gas	55-56	23-24	0.038-0.039
propane	50.0	25.4	0.093
butane	49.5	28.7	0.124
gasoline	56.5 45-55
peat	25.0
lignite	25-30
bituminous coal	30-35
anthracite	35-38

• Different fuels have different fuel densities. Although bituminous and anthracite coal is the most fuel dense.
• Industries tend to have constant energy demand. Humans tend to demand extra power between 18:00 and the time they go to sleep.

8.3.3 Discuss the relative advantages and disadvantages associated with the transportation and storage of fossil fuels.

Considerations:

• Location of the reserve- distance from power stations or to means of transport
• Construction and mining costs
• Cost of towns and services to house workers and families
• Price obtained for the fuel
• Energy density of the fuel
• Life time of the reserve
• Environmental costs by government regulation

Fuels can be transported by truck, rail or ship. Gas can additionally be transported by pipes. Pipes are disadvantageous because pipelines are unsightly and there is a possibility of leakages and explosions. Shipping oil is disadvantageous because of the possibility of oil slicks due to sinking and leaking of ships. Containers oil also have been known to explode. Coal mines are often located close to power stations and steel mines and docks for the purposes of energy production, coking, and transport to other locations respectively. Coal of higher rank advance are safer to transport and store.

8.3.4 State the overall efficiency of power stations fueled by different fossil fuels.

Only approximate values are required.

Efficiency of fossil fuels is determined by fuel type, the load factor, and employed technology.

The fuel density depends on the type of fuel. Conventional coal obtain efficiencies from 33-39%. Gas-powered obtain efficiencies from 33-49%.

Load factor indicates the electricity used by consumers by the formula
$$$${{{Peak Load}} \over {{Average Load}}} \right)$$$$ Conventional coal fired power satiations obtain an efficiency range of 33-39%. Higher efficiencies can be obtained by combined cycle plants such as CHP (combined heat and power) plants. These plants use surplus heat from a gas turbine to produce steam to turn a steam drive. Efficiencies over 50% can be achieved.

8.3.5. Describe the environmental problems associated with the recovery of fossil fuels and their use in power stations.

Coal

• Coal can be obtained through underground mines (tunneling) or open cut or strip mining.
• Cons of Underground mines:
  • More dangerous and more expensive
  • Mines must be ventilated so that poisonous and flammable gases
  • Particulate matter has to be pumped to the surface
  • There are accidents due to fires and mine cave-ins
  • Cave-ins in discontinued mines have caused hazards to land and surface structures above the mines
  • Miners are at risk of black lung disease

Fig. 1 Schematic Diagram of an Underground Coal Mine

Strip mines

Cons of strip mines

• Top soul is removed
• Over burdens the rock strata
• If the land is not reclaimed within short periods of time, water erosion can occur
• Sulfur deposits form acid

Pros of strip mines

• Coal can be extracted at a lower cost
• Low grade coals can be used
• Reclamation can occur by covering the area with topsoil and planting trees and grass
• Alternatively, the land is popularly used as garbage dumps

Crude Oil and Natural Gas

Expensive compared to coal mining

• Geographical mapping, and geophysical seismic exploration, and geochemical surveys, core sampling for botanical microorganisms, and drill prospecting, offshore engineering and other facilities can cost around 10 billion dollars
• Offshore exploration causes little effect on the environment (though economically costly)
• Modern air guns have little harmful effect on marine life (as opposed to dynamite formerly used for seismic exploration)
• Environment damage can still be caused by oil blowouts when the pressure of reservoir exceeds the pressure of the drill hole.

The key problem with the burning of fossil fuels is the release of pollutants. Carbon dioxide and carbon monoxide are major pollutants introduced by fossil-fueled power stations. Carbon monoxide is a poisonous gas that reduces the blood’s capability of transporting Oxygen. Carbon Dioxide is a green house gas that contributes to global warming. Other major pollutants are sulfur dioxide and oxides of nitrogen. Power stations can reduce emissions in the form of silica and metallic oxides, silicates, and sulfates. Using electrostatics, much of this matter can be removed so that it doe not enter the atmosphere.

Fig. 2 Schematic Diagram of an Electrostatic Precipitator

Sources

Kerr and Ruth
Fig. 1- Encyclopedia Britannica, Coal Mine
Fig. 2- Allied Environmental Technologies